The present invention relates to a safety belt arrangement and more particularly to a safety belt arrangement for use in restraining a passenger in a motor vehicle, such as a motor car.
It has been proposed to provide safety belts to restrain passengers within motor vehicles, such as motor cars. Conventionally such safety belts are associated with retractor reels which serve to retract the belt and maintain a slight tension in the belt. The retractor reel usually incorporates a locking mechanism which locks the reel to prevent belt being paid out from the reel in the event that an accident arises. Such a locking mechanism may respond either to severe deceleration of the vehicle, and/or to belt being withdrawn from the reel at greater than a predetermined rate.
It has been found desirable to provide, in association with such safety belts, a pre-tensioner adapted to apply a tension to the belt, in the event that an accident situation should arise. Since the locking arrangement present in a conventional retractor reel takes some time to be actuated, it is often the case that a certain length of safety belt has been paid out, from the reel, before the locking mechanism serves to lock the reel. The length of safety belt that has been paid out may be sufficient to permit the passenger restrained by the safety belt to travel forwardly, relative to his seat, which means that the passenger may then be in a position where he can hit the windscreen of the motor vehicle with his head. However, if a pre-tensioner is provided, when an accident situation is sensed, a tension is applied to the safety belt which serves to prevent this happening, retaining the passenger firmly in his seat.
Various types of pre-tensioner have been proposed before, and certain pre-tensioners have been proposed which serve to rotate the shaft of the retractor reel in order to wind a length of safety belt on to the reel when an accident situation arises.
U.S. Pat. No. 4,423,846A discloses a pre-tensioner of this type. When an accident situation is sensed a force is applied to a cable which is applied to a drum. The drum is provided with elements which, on rotation of the drum, engage fixed pegs and are thus moved to a condition where they engage a splined extension of the shaft of the retractor reel. Continued tension applied by the cable causes the shaft of the retractor reel to rotate, winding safety belt on to the shaft of the retractor reel. However, this movement of the drum also snaps the pegs. Thus if the elements become disengaged from the splined extension of the shaft there is nothing to re-engage them with the shaft. The described arrangement is relatively complex and difficult to assemble.